Low profile spinal tethering devices

ABSTRACT

Methods and devices for treating spinal deformities are provided. In one exemplary embodiment, a low-profile spinal anchoring device is provided for receiving a spinal fixation element, such as a tether, therethrough. The device generally includes a staple body that is adapted to seat a spinal fixation element, a fastening element for fixing the staple body to bone, and a locking assembly for coupling a spinal fixation element to the staple body. In one embodiment, the locking assembly includes a washer that is adapted to couple to the staple body such that the spinal fixation is disposed therebetween, and a locking nut that is adapted to engage the staple body to mate the washer to the staple body.

BACKGROUND

Spinal deformities, which include rotation, angulation, and/or curvatureof the spine, can result from various disorders, including, for example,scoliosis (abnormal curvature in the coronal plane of the spine),kyphosis (backward curvature of the spine), and spondylolisthesis(forward displacement of a lumbar vertebra). Early techniques forcorrecting such deformities utilized external devices that apply forceto the spine in an attempt to reposition the vertebrae. These devices,however, resulted in severe restriction and in some cases immobility ofthe patient. Furthermore, current external braces have limited abilityto correct the deformed spine and typically only prevent progression ofthe deformity. Thus, to avoid this need, several rod-based techniqueswere developed to span across multiple vertebrae and force the vertebraeinto a desired orientation.

In rod-based techniques, one or more rods are attached to the vertebraeat several fixation sites to progressively correct the spinal deformity.The rods are typically pre-curved intraoperatively to a desired adjustedspinal curvature. Wires as well as bone screws can be used to pullindividual vertebra toward the rod. Once the spine has beensubstantially corrected, the procedure typically requires fusion of theinstrumented spinal segments.

While several different rod-based systems have been developed, they tendto be cumbersome, requiring complicated surgical procedures with longoperating times to achieve correction. Further, intraoperativeadjustment of rod-based systems can be difficult and may result in lossof mechanical properties due to multiple bending operations. Therigidity and permanence of rigid rod-based systems can also hinder orprevent growth of the spine and they generally require fusion of manyspine levels, drastically reducing the flexibility of the spine. Inaddition to excessive rigidity, other drawbacks with current devicesinclude dislodgement and a high profile.

Accordingly, there remains a need for improved methods and devices forcorrecting spinal deformities and, in particular, there remains a needfor low-profile, flexible non-fusion spinal correction methods anddevices.

SUMMARY

The present invention provides methods and devices for treating spinaldeformities. In one exemplary embodiment, a spinal anchoring device isprovided and it includes a staple body, a fastening element, and alocking assembly. The staple body can be adapted to receive thefastening element for mating the staple body to bone, and to seat atether. The locking assembly can be applied to the staple body to engagethe tether and substantially prevent movement thereof relative to thedevice.

While the staple body can have a variety of configurations, in oneembodiment the staple body includes a central opening formedtherethrough and a pathway extending across the central opening forseating a tether. In an exemplary embodiment, the central openingincludes a substantially spherical surface formed therearound forseating a complementary spherical surface formed on the fasteningelement. The staple body can also include opposed arms extending fromopposed sides of a superior surface. The opposed arms can define thepathway therebetween. The configuration of the pathway can vary, but inone exemplary embodiment the pathway is non-linear, and more preferablyit is tortuous. In another embodiment, the opposed arms can includethreads formed on an external surface thereof for mating withcorresponding threads formed on the locking assembly.

The fastening element can also have a variety of configurations, but inone embodiment the fastening element is adapted to extend through acentral opening formed in the staple body to mate the staple body tobone. By way of non-limiting example, the fastening element can be abone screw having a head and a shank. In an exemplary embodiment, thehead of the bone screw includes a flange formed just distal to aproximal end of the shank of the bone screw and having a diameter thatis greater than a diameter of the central opening formed in the staplebody. The flange can also include a substantially spherical inferiorsurface that is adapted to correspond to a substantially sphericalsurface formed around the central opening of the staple body. The headof the bone screw can also include a proximal extension that is adaptedto extend into the pathway of the staple body. The proximal extensioncan include a recess formed therein for receiving a tool adapted todrive the bone screw into bone.

The locking assembly can also have a variety of configurations, but inone embodiment it is adapted to engage the staple body such that atether extending through the pathway extends between the lockingassembly and the staple body. In an exemplary embodiment, the lockingassembly includes a washer that is adapted to couple to the staple bodysuch that a tether extending through the pathway is positioned betweenthe washer and the staple body, and a locking nut that is adapted toengage the staple body to lock the washer to the staple body. While theshape of the washer can vary, one exemplary washer includes opposedopenings formed therethrough for receiving the opposed arms on thestaple body. The washer can also include a strut extending thereacrossand adapted to be positioned between the opposed arms. In otherexemplary embodiments, the locking assembly can be a nut, such as a setscrew, or a washer that is separate from the staple body, or that iscoupled to the staple body and movable between an open position and aclosed position.

In yet another embodiment, the spinal anchoring device can include adeformable clip that is adapted to be disposed around a tether andpositioned within the pathway such that the locking assembly is adaptedto deform the clip to engage the tether when the locking assembly ismated to the staple body.

In other embodiments, the staple, the fastening element, and/or thelocking assembly can include a tether-engaging feature formed thereon.In one exemplary embodiment, the tether-engaging features can be atleast one groove formed on the superior surface of the staple andpositioned in the pathway, and at least one complementary ridge formedon the locking assembly such that the at least one ridge and at leastone groove are adapted to engage a tether seated in the pathway. Inanother embodiment, the tether-engaging feature can be a head formed ona proximal end of the fastening element and adapted to extend into thepathway such that the head alters a path of a tether seated in thepathway. In yet another embodiment, the tether-engaging feature can be aprotrusion formed on an inferior surface of the locking assembly suchthat the protrusion is adapted to extend into a tether seated in thepathway.

An exemplary tether for use with a spinal anchoring device is alsoprovided and it is in the form of a substantially flat elongate memberhaving a cross-sectional width that is at least two times greater than across-sectional height. In an exemplary embodiment, the tether is formedfrom a biocompatible polymeric braided material, such as an ultra-highmolecular weight polyethylene, or poly(ethylene terephthalate). In otherembodiments, the tether can be formed from a bioabsorble material, suchas poly(L-lactic acid).

An exemplary spinal anchoring system is also provided, which includes asubstantially flat elongate tether, and an anchoring device that isadapted to mate to bone and that includes a pathway formed therethroughfor seating the substantially flat elongate tether such that the tetheris maintained in a substantially fixed position. In an exemplaryembodiment, the anchoring device includes a staple that is adapted topenetrate bone and defining the pathway, a fastening element that isadapted to mate the staple to bone, and a locking assembly that isadapted to engage the staple to maintain the tether in a substantiallyfixed position between the locking assembly and the staple.

In certain aspects, the anchoring device can include at least onetether-engaging feature that is adapted to extend into the pathway tomaintain the tether in a substantially fixed position. Thetether-engaging feature can be, for example, a clip that is adapted tobe disposed around the tether. In other embodiments, the tether-engagingfeature can be a ridge formed on an inferior surface of the washer forextending into at least one corresponding complementary groove formed ina superior surface of the staple. The ridge(s) and the groove(s) can beadapted to engage the tether therebetween.

Various tools for implanting spinal anchoring devices are also provided.In one exemplary embodiment, a tool is provided having an elongate shaftwith proximal and distal ends and an inner lumen extending therebetween.The distal end can include opposed deflectable members separated by anelongate slot, and the opposed deflectable members can include asubstantially cylindrical portion having a recess formed in a distalsurface thereof. In an exemplary embodiment, the recess is substantiallyrectangular, and it extends between the opposed deflectable members suchthat it separates a distal-most portion of the opposed deflectablemembers.

In another embodiment, an inserter system is provided having a fastenerinserter tool with an elongate shaft having a substantially cylindricalmember formed on the distal end thereof and including opposed arms, anda wrench having a hollow elongate shaft that is adapted to be slidablydisposed over the fastener inserter tool, and having a distal end with asocket member formed thereon and adapted to receive a locking element.In one embodiment, the socket member of the wrench includes a hexagonalsocket formed therein.

Methods for correcting spinal deformities are also provided, and in oneexemplary embodiment the method includes implanting an anchoring elementin bone, positioning a substantially flat elongate tether through theanchoring element, and applying a locking element to the anchoringelement to engage the tether. In one embodiment, the anchoring elementcan be implanted in bone by impacting a staple into bone, and insertinga fastening element through the staple and into a bone hole to mate thestaple to bone. In another embodiment, the anchoring element can beimplanted in bone by inserting the fastening element into a bone hole todrive a staple into bone. In yet another embodiment, a locking elementcan be applied to the anchoring element by positioning a washer aroundopposed arms of staple of the anchoring element such that the tether ispositioned between the washer and the staple. A locking nut can then bemated to the opposed arms.

In another exemplary embodiment, there is provided a method forcorrecting spinal deformities, which includes impacting at least onebone-penetrating member formed on an inferior surface of a staple bodyinto a vertebra, inserting a fastening element through the staple bodyand into the vertebrae to attach the staple to the vertebra, positioninga tether on a superior surface of the staple such that the tetherextends over a head of the fastening element, and applying a lockingmechanism to the staple to maintain the tether in a substantially fixedposition relative to the staple.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a perspective view of one exemplary embodiment of a spinalanchoring device;

FIG. 1B is a cross-sectional view of the spinal anchoring device shownin FIG. 1A;

FIG. 2A is a top perspective view of a staple body of the spinalanchoring device shown in FIG. 1A;

FIG. 2B is a bottom perspective view of the staple body shown in FIG.2A;

FIG. 3 is a perspective view a fastening element of the spinal anchoringdevice shown in FIG. 1A;

FIG. 4A is a top perspective view of a washer that forms part of thelocking assembly of the spinal anchoring device shown in FIG. 1A;

FIG. 4B is a bottom perspective view of the washer shown in FIG. 4A;

FIG. 5 is a perspective view of a locking nut that forms part of thelocking assembly of the spinal anchoring device shown in FIG. 1A;

FIG. 6 is a perspective view of one exemplary embodiment of a flatflexible tether;

FIG. 7A is a perspective view of another exemplary embodiment of aspinal anchoring device having a tether coupled thereto by a lockingmechanism;

FIG. 7B is a cross-sectional view of the spinal anchoring device shownin FIG. 7A;

FIG. 7C is a perspective view of the spinal anchoring device shown inFIG. 7A without the tether and the locking mechanism coupled thereto;

FIG. 7D is a perspective view of the spinal anchoring device shown inFIG. 7C showing the tether extending through a pathway formed therein;

FIG. 7E is a perspective view of the spinal anchoring device shown inFIG. 7D showing the locking mechanism about to be coupled thereto andhaving a locking nut and a washer;

FIG. 7F is a perspective view of the spinal anchoring device shown inFIG. 7E showing the locking nut and washer of the locking mechanismcoupled to one another;

FIG. 8 is a perspective view of another embodiment of a washer for usewith a spinal anchoring device;

FIG. 9A is a perspective, disassembled view of another exemplaryembodiment of a spinal anchoring device having a clip for engaging atether extending therethrough;

FIG. 9B is a perspective, assembled view of the spinal anchoring deviceshown in FIG. 9A having the tether extending therethrough;

FIG. 9C is a cross-sectional view of a portion of the spinal anchoringdevice shown in FIG. 9A with the locking mechanism about to be coupledthereto;

FIG. 9D is a cross-sectional view of a portion of the spinal anchoringdevice shown in FIG. 9C with the locking mechanism coupled thereto;

FIG. 10A is a perspective, disassembled view of yet another exemplaryembodiment of a spinal anchoring device having a tether extendingtherethrough and having a two-piece locking element;

FIG. 10B is a perspective, partially assembled view of the spinalanchoring device shown in FIG. 10A having the tether extendingtherethrough with a twist formed therein;

FIG. 10C is a perspective, fully assembled view of the spinal anchoringdevice shown in FIG. 10B having the tether extending therethrough;

FIG. 11A is an illustration showing a staple inserter tool about toimplant a staple of a spinal anchoring device in a vertebra;

FIG. 11B is a perspective view of the staple inserter tool shown in FIG.11A;

FIG. 11C is a perspective view of a distal end of the staple insertertool shown in FIG. 11B with a staple coupled thereto;

FIG. 12A is an illustration showing an awl inserted through the stapleinserter tool and staple shown in FIG. 11A for preparing a bone hole;

FIG. 12B is a perspective view of the awl shown in FIG. 12A;

FIG. 12C is a perspective view of a distal end of the awl shown in FIG.12B inserter through the staple inserter tool and staple shown in FIG.12A;

FIG. 13A is an illustration showing a tap about to be inserted throughthe staple implanted in the vertebrae for forming threads in the bonehole prepared by the awl;

FIG. 13B is a perspective view of the tap shown in FIG. 13A;

FIG. 14 is an illustration showing a driver tool about the implant afastening element through the staple and into the bone hole;

FIG. 15 is an illustration showing two spinal anchoring devicesimplanted in two vertebrae;

FIG. 16A is an illustration showing a tether positioned relative to thetwo spinal anchoring devices implanted in the vertebrae shown in FIG.15, and showing a fastener inserter tool about to apply a fasteningelement to one of the spinal anchoring devices;

FIG. 16B is a perspective view of the fastener inserter tool shown inFIG. 16A;

FIG. 16C is a perspective view of a distal portion of the fastenerinserter tool shown in FIG. 16B showing a fastening element coupledthereto;

FIG. 17A is an illustration showing the fastening element applied to thespinal anchoring device using the fastener inserter tool shown in FIG.16A, and showing a wrench inserted over the driver;

FIG. 17B is an illustration showing the wrench of FIG. 17A being rotatedrelative to the drive to rotate a locking nut of the locking mechanism;

FIG. 17C is a perspective view of the wrench shown in FIGS. 17A and 17B;and

FIG. 18 is an illustration showing a tether extending between andcoupled to two spinal anchoring devices implanted in two vertebrae.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

In one exemplary embodiment, a low-profile spinal anchoring device isprovided for receiving a spinal fixation element, such as a tether,therethrough. In use, several spinal anchoring devices can be implantedin several adjacent vertebrae, and the tether can be coupled to thespinal anchoring devices to halt growth of the spine on the side wherethe tether is applied. By halting the growth of the spine on the convexside of the deformity, subsequent growth of the spine on the concaveside will cause the deformity to self-correct, thus gradually providingthe correction while allowing the patient's overall height to increase.The methods and devices can, however, be used in a variety of otherspinal applications. By way of non-limiting example, the spinalanchoring devices and/or tethers disclosed herein can be used forintraoperative deformity correction with subsequent fusion, as taught byDr. A. F. Dwyer in the 1960's and 70's (Clin Orthop Rel Res 93, pp.191-206, 1973, and J Bone Joint Surg 56B, pp. 218-224). In addition,they can be used for posterior dynamization to function as adecompressive device for stenosis and/or an adjunct to an intervertebraldisc to unload the facets of the vertebra. A variety of exemplarymethods and tools for implanting a spinal anchoring device are alsoprovided.

FIGS. 1A and 1B illustrate one exemplary embodiment of a spinalanchoring device 10. As shown, the device 10 generally includes a staplebody 12 that is adapted to seat a spinal fixation element, a fasteningelement 14 for fixing the staple body 12 to bone, and a locking assemblyfor coupling a spinal fixation element to the staple body 12. In theillustrated exemplary embodiment, the locking assembly includes a washer16 that is adapted to couple to the staple body 12 such that the spinalfixation element is disposed therebetween, and a locking nut 18 that isadapted to engage the staple body 12 to mate the washer 16 to the staplebody 12. The locking assembly can, however, have a variety of otherconfigurations and it can be separate from the staple body or coupled tothe staple body.

The staple body 12 is shown in more detail in FIGS. 2A and 2B, and itcan have a variety of configurations. In the illustrated exemplaryembodiment, it has a substantially annular shape with a superior surface12 s, an inferior surface 12 i, and a central opening 12 o formedtherethrough. The inferior surface 12 i of the staple body 12 caninclude one or more bone-engaging members 26 formed thereon and adaptedto extend into bone to prevent rotational movement of the staple 12 whenthe staple 12 is implanted. FIG. 2B illustrates multiple bone-engagingmembers 26 formed on and extending distally from the inferior surface 12i of the staple 12. The bone-engaging members 26 are in the form ofspikes that are adapted to extend into bone, however they can have avariety of other shapes. As is further shown, the bone-engaging members26 can vary in size. In use, a mallet or other device can be used toapply a force to the staple 12 to impact the spikes into bone at thedesired implant site, or a fastening element can be used to drive thestaple 12 into bone, as will be discussed in more detail below.

The central opening 12 o in the staple body 12 can be adapted to receivea fastening element 14 therethrough to allow the fastening element 14 tomate the staple body 12 to bone. While the configuration of the centralopening 12 o can vary depending on the configuration of the fasteningelement 14, as will be discussed in more detail below with respect toFIG. 3, in one exemplary embodiment the central opening 12 o has asubstantially spherical, concave surface 22 formed therearound forseating a substantially spherical mating surface of the fasteningelement 14. The spherical surface 22 allows the fastening element 14 tobe polyaxially movable with respect to the staple body 12, therebyallowing the fastening element 14 to be inserted into bone at an anglewith respect to the staple body 12. A person skilled in the art willappreciate that the central opening 12 o can have a variety of otherconfigurations, and that the staple body 12 can include a fasteningelement integrally formed therewith or mated thereto. For example, thestaple body 12 can be swaged such that the fastening element 14 isintegrated to the staple body 12 while allowing the fastening element 14to rotate with respect to the staple body 12 to allow insertion intobone.

As further shown in FIGS. 2A and 2B, the staple body 12 can also includeopposed arms 20 a, 20 b formed on the superior surface 12 s. As will bediscussed in more detail below, the arms 20 a, 20 b can be adapted tocouple to the locking assembly, thus the arms 20 a, 20 b can include amating element formed thereof for mating with at least a portion of thelocking assembly. As shown in FIGS. 2A and 2B, each arm 20 a, 20 b caninclude threads 21 a, 21 b formed on an external surface thereof. Thethreads 21 a, 21 b can extend along the entire length of each arm 20 a,20 b, or they can be formed only on a terminal portion of the arms 20 a,20 b, as shown. In one exemplary embodiment of the invention, the matingelements can have a square thread pattern. The particular configurationof each arm 20 a, 20 b can vary depending on the particularconfiguration of the locking mechanism, and a variety of other matingelements can be used to engage the locking assembly.

In use, the staple body 12 is adapted to seat a spinal fixation element.Accordingly, the superior surface 12 s of the staple body 12 can definea pathway 12 p formed between the opposed arms 20 a, 20 b. The pathway12 p can be adapted to seat a spinal fixation element between theopposed arms 20 a, 20 b such that the spinal fixation element extendsacross the superior surface 12 s and the opening 12 o. As a result, whenthe locking assembly is applied to the staple body 12, the spinalfixation element can be engaged between the locking assembly and thestaple body 12 to maintain the spinal fixation element in asubstantially fixed position. A person skilled in the art willappreciate that the pathway 12 p can have a variety of configurations,and it can be linear or non-linear such that it changes direction, istortuous, has curves or bends, etc.

The superior surface 12 s of the staple body 12 can also includefeatures to facilitate engagement of a spinal fixation element betweenthe locking assembly and the staple body 12. By way of non-limitingexample, the superior surface 12 s can include one or more protrusions(not shown) formed thereon and adapted to extend into a spinal fixationelement, such as a tether, an exemplary embodiment of which will bedescribed in more detail below. In other embodiments, the superiorsurface 12 s can include one or more ridges or grooves formed thereonfor receiving one or more complementary grooves or ridges formed on thelocking assembly. FIG. 2A illustrates two grooves 24 a, 24 b formed onopposed sides of the superior surface 12 s of the staple body andpositioned within the pathway 12 p. The grooves 24 a, 24 b are adaptedto receive complementary ridges formed on the washer of the lockingassembly, as will be discussed in more detail with respect to FIGS. 4Aand 4B.

As previously mentioned, the staple body 12 can be adapted to receive afastening element 14 through the central opening 12 o. While thefastening element 14 can have a variety of configurations, FIG. 3illustrates one exemplary fastening element 14 that is in the form of abone screw having a head 14 b and a threaded shaft 14 a that is adaptedto extend into bone. The thread form of the threaded shaft 14 a ispreferably adapted for fixation in cancellous bone, and in certainexemplary embodiments the surface of the threaded shaft 14 a can betreated to promote bone apposition. Techniques known in the art forpromoting bone apposition include anodization and coating with materialscontaining calcium phosphate, collagen, bone growth factors, etc. Thehead 14 b of the fastening element 14 can vary in shape and sizedepending on the configuration of the staple body 12, but in theillustrated exemplary embodiment the head 14 b includes a flange 30 thatis adapted to sit within the opening 12 o in the staple body 12. Theflange 30 can have a diameter that is greater than a diameter of thecentral opening 12 o formed in the staple body 12 to prevent passage ofthe flange 30 therethrough. The flange 30 can also include asubstantially spherical inferior surface (not shown) to allow thefastening element 14 to move polyaxially with respect to the staple body12, as previously discussed.

The head 14 b of the fastening element 14 can also include a proximalextension 32 extending proximally from the flange 30. The proximalextension 32, which can be formed integrally with the shaft 14 a of thebone screw 14, can include a recess 34 formed therein for receiving atool adapted to drive the fastening element 14 into bone. The recess 34can have any shape and size, but in the illustrated embodiment it has ahexagonal shape for receiving a hexagonal driver tool.

In use, when the fastening element 14 is disposed through the centralopening 12 o of the staple body 12, the proximal extension 32 can extendinto the pathway 12 p that seats a spinal fixation element, such as aflexible tether. Such a configuration is effective to create a bend orkink in the tether to substantially prevent sliding movement of thetether, or to otherwise facilitate engagement of the tether between thestaple body 12 and the locking assembly. A person skilled in the artwill appreciate that, while a polyaxial bone screw 14 is shown, the bonescrew can be monoaxial or it can have a variety of other configurations.Other techniques for attaching the staple body 12 to bone may also beused.

As discussed with respect to FIGS. 1A and 1B, the spinal anchoringdevice 10 can also include a locking assembly that is adapted to mate tothe staple body 12 to maintain a spinal fixation element, such as atether, in a fixed position relative to the staple body 12. Theconfiguration of the locking assembly can vary, and it can be formedfrom a single component or from multiple components. The lockingassembly can also be separate from the staple body 12, or it can becoupled to the staple body and movable between an unlocked and a lockedconfiguration. In the illustrated exemplary embodiment, the lockingassembly includes a washer 16 and a locking nut 18. The washer 16 isadapted to couple to the staple body 12 such that the tether ispositioned between the washer 16 and the superior surface 12 s of thestaple body 12, and the locking nut 18 can be adapted to mate to thearms 20 a, 20 b of the staple body 12 to lock the washer 16 to thestaple body 12, thereby locking the tether therebetween.

An exemplary washer 16 is shown in more detail in FIGS. 4A and 4B, andas shown the washer 16 includes a generally annular member 35 with astrut 36 spanning across the annular member 35. The annular member 35 isadapted to be positioned around the opposed arms 20 a, 20 b of thestaple body 12, and thus it can have a size that substantiallycorresponds to the size of the annular portion of the staple body 12.The strut 36 is adapted to be received between the opposed arms 20 a, 20b and positioned within the pathway 12 p of the staple body 12 tosubstantially prevent rotation of the washer 16 with respect to thestaple body 12. Such a configuration is particularly advantageous inthat the tether is protected from high, damaging shear forces. The strut36 can be adapted to merely facilitate positioning of the washer 16 withrespect to the staple body 12, or it can be adapted to engage a spinalfixation element, such as a tether, disposed within the pathway 12 p. Inan exemplary embodiment, as shown, the strut 36 includes opposed legs 36a, 36 b that extend outward from the annular member 35, and a connectingmember 36 c that extends between the opposed legs 36 a, 36 b. Such aconfiguration allows the connecting member 36 c to be positioned adistance apart from the staple body 12, thereby allowing the extension32 formed on the head 14 b of the fastening element 14 to extend intothe pathway 12 p without abutting against the connecting member 36 c ofthe strut 36. The height of the opposed legs 36 a, 36 b can, however, bevaried based on the size of the spinal fixation element, and based onthe intended use and whether the connecting member 36 c is to engage thespinal fixation element. Moreover, the strut 36 itself can vary in shapeand size depending on the configuration of the staple body 12 and thespinal fixation element adapted to be disposed therein.

As previously discussed with respect to the staple body 12, the washer16 can also include features to facilitate engagement of a spinalfixation element, such as a flexible tether, between the staple body 12and the washer 16. As shown in FIG. 4B, which illustrates the bottom ofthe washer 16, the annular member 35 of the washer 16 can includeopposed ridges 38 a, 38 b formed thereon and adapted to be received withthe complementary grooves 24 a, 24 b formed in the staple body 12, asshown in FIG. 2A. The ridges 38 a, 38 b are preferably formed adjacentto the legs 36 a, 36 b of the strut 36 such that when the strut 36 isreceived between the opposed arms 20 a, 20 b of the staple body 12, theridges 38 a, 38 b are aligned with and extend into the grooves 24 a, 24b. In use, when a flexible tether is disposed between the staple body 12and the washer 16, the ridges 38 a, 38 b and grooves 24 a, 24 b willform a kink in the tether, thereby facilitating engagement such that thetether will be maintained in a substantially fixed position with respectto the device 10. A person skilled in the art will appreciate that avariety of other features can be used to facilitate engagement of aspinal fixation element. By way of non-limiting example, the washer 16can include one or more protrusions or spikes formed on the surfacethereof for abutting or extending into the tether.

As previously noted, the locking assembly can also include a locking nut18 that is adapted to lock the washer 16 to the staple body 12. Anexemplary locking nut 18, shown in more detail in FIG. 5, has agenerally annular shape. The locking nut 18 can, however, have anexternal surface that is hexagonal or of some other shape that allowsthe locking nut 18 to be engaged by a wrench or other driver tool forrotating the locking nut 18. In use, the locking nut 18 is adapted to bepositioned around and to mate to the opposed arms 20 a, 20 b on thestaple body 12. Accordingly, as previously indicated, the locking nut 18can include threads 18 a formed therein for mating with thecorresponding threads 21 a, 21 b formed on the arms 20 a, 20 b of thestaple body 12. In an exemplary embodiment, the locking nut 18 can beswaged to the washer 16 during manufacturing to integrate the two yetallow the nut 18 to be rotated with respect to the washer 16 duringtightening of the closure mechanism. A variety of other matingtechniques can also be used to mate the locking nut 18 to the body,including a snap-fit connection, an interference fit, etc.

A person skilled in the art will appreciate that the locking assemblycan have a variety of other configurations. For example, rather thanusing a locking nut 18, the washer 16 itself can be adapted to mate tothe staple body 12. The washer 16 can be a separate component, or it canbe mated to the staple body 12 and movable between an open or unlockedposition and a closed or locked position. For example, the washer 16 maybe connected to the staple body 12 by a hinge or the like.Alternatively, the locking nut 18 can be used without the washer 16 tofix the tether to the staple body 12. In other embodiments, the lockingnut 18 can be in the form of an inner set screw that mates to an innersurface of the legs 20 a, 20 b of the staple body 12.

Referring back to FIGS. 1A and 1B, in use the device 10 is adapted toreceive and engage a spinal fixation element. While a variety of spinalfixation elements can be used, including both flexible and rigidfixation elements, in an exemplary embodiment the spinal fixationelement is a flexible tether. FIG. 6 illustrates one exemplaryembodiment of a flexible tether 50, and as shown the tether 50 issubstantially flat or planar. More particularly, the tether 50 can havea cross-sectional width w that is greater than a cross-sectional heighth. In one exemplary embodiment, the width w can be at least two timesgreater than the height h. By way of non-limiting example, the width wcan be in the range of about 4 mm to 8 mm, and preferably about 6 mm,and the height h can be in the range of about 0.5 mm to 2.5 mm, andpreferably about 1.5 mm. Alternatively, the tether can have any numberof different cross-sections, including square and round. In somepreferred embodiments, the tether cross-section is square or roundinitially but then becomes flattened as the closure mechanism istightened.

The tether 50 can be made using a variety of techniques, but in oneexemplary embodiment it is made using a flat braiding process. Othersuitable processes include, for example, a 3-D weaving process. Theproperties of the tether 50 can also vary, but in an exemplaryembodiment the tether has a tensile strength in the range of about 1 GPato 5 GPa, and preferably about 3 GPa, and a tensile modulus in the rangeof about 10 GPa to 200 GPa, and preferably about 100 GPa.

The materials used to form the tether can also vary, but suitableexemplary materials include polymers such as ultra-high molecular weightpolyethylene (UHMWPE). Examples of commercially available UHMWPE fibersinclude Dyneema® (manufactured by DSM) and Spectra® (manufactured byAllied Signal). Other materials that can be used, for example, includepolyethylene terephthalate (PET), nylon, Kevlar®, carbon, etc. In otherembodiments, the tether 50 can be made from a combination of materials,for example UHMWPE fibers combined with PET fibers. The tether 50 canalso be made from bioabsorbable materials, such as poly(L-lactic acid)or other high strength, slowly degrading materials known in the art.

In use, the tether 50 can be positioned within the pathway 12 p of thestaple body 12 after the staple body 12 is implanted in bone. Animpacting tool for driving the staple body 12 into bone can be used toimplant the staple 12. The fastening element 16 can then be insertedtherethrough to fix the staple body 12 to the bone. Alternatively, adriver tool can be used to drive the fastening element 16 into bone,thereby driving the staple body 12 into bone. When the tether 50 ispositioned in the pathway 12 p, the tether 50 will extend between thelegs 20 a, 20 b and up around the extension 32 on the fastening element16. The washer 14 can then be placed around the legs 20 a, 20 b of thestaple body 12, and the locking nut 16 can be threaded onto the legs 20a, 20 b to lock the washer 16 to the staple body 12, thereby locking thetether 50 to the device 10. The ridges 38 a, 38 b on the washer 16 willextend toward the grooves 24 a, 24 b on the staple body 12, therebycreating a kink or bend in the tether 50, further facilitatingengagement of the tether 50 between the washer 16 and the staple body12. Other exemplary methods and tools for implanting the spinalanchoring device 10 will be discussed in more detail below.

FIGS. 7A-7F illustrate another exemplary embodiment of a spinalanchoring device 100. The device 100 is similar to spinal anchoringdevice 10 shown in FIG. 1A, and it includes a staple body 112, afastening element 114, a washer 116, and a locking nut 118. In thisembodiment, the washer 116 does not include a strut. Rather, the washer116 includes opposed legs 136 a, 136 b that extend from a substantiallyplanar annular body 135. The legs 136 a, 136 b each include a flange 137a, 137 b formed on the terminal end thereof and extending in opposeddirections from one another. The flanges 137 a, 137 b are adapted toengage the locking nut 118 to allow the washer 116 and locking nut 118to be mated to one another prior to mating the locking assembly to thestaple body 12. The legs 136 a, 136 b can be flexible to allow thelocking nut 118 to be inserted there over and mated to the washer 116.

FIGS. 7C-7F illustrate assembly of the device, and as shown the tether50 is positioned in the pathway in the staple body 112. The washer 116and locking nut 118 can be mated to one another, as shown in FIG. 7F,and then they can be mated to the staple body 112. The matingconfiguration of the washer 116 and the locking nut 118 allows thelocking nut 118 to rotate freely with respect to the washer 116, therebyallowing the washer 116 to maintain a substantially fixed position withrespect to the staple body 112, while the locking nut 118 is threadedonto the arms 120 a, 120 b of the staple body 112. This is particularlyadvantageous as the legs 136 a, 136 b of the washer 116 will bepositioned between the arms 120 a, 120 b of the staple body 112, therebypreventing the washer 116 from rotating with respect to the staple body112.

FIG. 8 illustrates another exemplary embodiment of a washer 160 for usewith a spinal anchoring device. In this embodiment, the washer 160 has asubstantially planar annular member 162 with a substantially planarstrut 164 extending thereacross. The washer 160 also includes atether-engaging protrusion 166 formed thereon. In use, the opposed armsof a staple body, such as arms 20 a, 20 b of staple 12 shown in FIG. 1A,are adapted to be received within the annular member 162 such that thestrut 164 extends between the opposed arms 20 a, 20 b. The planarconfiguration of the washer 160 will cause the washer 160 to engage thetether 50 between the staple body 12 and the washer 160. As a result,the protrusion 166 formed on the strut 164 will abut and deform thetether 50, thereby engaging the tether 50 to substantially preventmovement of the tether 50 with respect to the device. Since the washer160 is substantially planar, the head of the fastening element used withthe staple body preferably does not extend into the tether pathwayformed in the staple body, as such a configuration would cause the strut164 to abut against the head of the fastening element.

FIGS. 9A-9D illustrate yet another embodiment of a spinal anchoringdevice 200. In general, the device 200 includes a staple body 212,fastening element 214, and a locking nut 218 that are similar to staplebody 12, fastening element 14, and locking nut 18 shown in FIG. 1A. Inthis embodiment, rather than using a washer 16 to engage a tether 50, aclip 216 is used to engage the tether 50. The clip 216 can be adapted tobe disposed around a spinal fixation element, such as tether 50, and itcan be adapted to be positioned within the pathway of the staple body 12and disposed between the staple body 12 and the locking nut 218. Whilethe shape and size of the clip 216 can vary depending on the shape andsize of the spinal anchoring device used therewith, in an exemplaryembodiment the clip 216 has a substantially elongate shape with opposedarms 216 a, 216 b that define a track or recess therebetween for seatingthe tether 50.

In use, the arms 216 a, 216 b can extend around the tether 50 to engagethe tether 50. In an another exemplary embodiment, the clip 216 can beformed from a pliable or deformable material to allow the clip 216 todeform around the tether 50 when the locking nut 18 is applied to thestaple body 12. FIG. 9C illustrates the clip 216 disposed around thetether 50 with the locking nut 218 about to be mated to the staple body212. FIG. 9D illustrates the locking nut 218 threaded onto the staplebody 212, and as shown the clip 216 is deformed by the locking nut 218such that the clip 216 engages the tether 50 to prevent sliding movementthereof relative to the device 200. In another embodiment, the clip is adeformable tube that serves to protect the tether while tightening thelocking nut. In yet another embodiment, the clip does not deform upontightening the locking nut, thereby allowing the tether to slide withinthe closure mechanism.

FIGS. 10A-10C illustrate yet another exemplary embodiment of a spinalanchoring device 300. The device 300 includes a staple body 312 andfastening element 314 that are similar to staple body 12 and fasteningelement 14 shown in FIG. 1A. However, the staple body 312 does notinclude opposed arms formed thereon, but rather has a substantiallyplanar superior surface 312 s, and the fastening element 314 has asubstantially planar head 314 a formed thereon such that the head 314 ais co-planar with, or recessed with respect to, the superior surface 312s of the staple body 312. The staple body 312 also includes severalmating elements formed thereon for mating to the locking assembly. Whilethe mating elements can have a variety of configurations, in theexemplary embodiment illustrated in FIGS. 10A-10C the staple body 312includes cut-outs 312 a, 312 b, 312 c, 312 d formed therein forreceiving tabs formed on the locking mechanism.

As shown, the locking mechanism includes first and second members 316 a,316 b that are adapted to mate to opposed sides of the superior surface312 s of the staple body 312 to engage the tether 50 therebetween. Whilenot shown, the first and second members 316 a, 316 b can be integrallyformed as a single member that mates to the staple body 312. Eachmembers 316 a, 316 b can have a substantially semi-circular shape withmating elements formed thereon for engaging the complementarycorresponding mating elements formed on the superior surface 312 s ofthe staple body 312. In the illustrated exemplary embodiment, themembers 316 a, 316 b each includes two tabs formed thereon. Only twotabs 317 a, 317 b are shown formed on the first member 316 a. Each tab317 a, 317 b is adapted to extend into the corresponding cut-out 312 a,312 b, 312 c, 312 d formed in the staple body 312 to engage the staplebody 312 by a snap-fit or interference fit.

In use, a tether 50 can be positioned across the staple body 312, e.g.,in the pathway, and the first and second members 316 a, 316 b can thenbe mated to the staple body 312, as shown in FIG. 10C, to engage thetether 50 therebetween. In an exemplary embodiment, each member 316 a,316 b is positioned such that the tabs 317 a, 317 b are positioned onopposed sides of the tether 50, thereby allowing the annular portion ofthe members 316 a, 316 b to engage the tether 50. As is further shown inFIGS. 10B and 10C, the tether 50 can optionally be twisted to form oneor more twists 51 between the two members 316 a, 316 b, thereby furtherpreventing slidable movement of the tether 50 with respect to the device300.

A person skilled in the art will appreciate that the spinal anchoringdevice can have a variety of other configurations, and it can include acombination of various features disclosed herein, as well as otherfeatures to facilitate engagement of a spinal fixation element, such asa tether.

An exemplary method for implanting a spinal anchoring device is alsoprovided. While the method can be performed using a variety of differentspinal anchoring devices, the method is described in connection withspinal anchoring device 10. Referring first to FIG. 11A, a stapleinserter 400 is shown for inserting the staple body 12 of device 10 intobone. The exemplary staple inserter 400, shown in more detail in FIG.11B, includes a generally elongate hollow shaft 402 having a proximalend with a handle 404 formed thereon, and a distal end with astaple-engaging member 406 formed thereon. The staple-engaging member406 is adapted to engage the staple body 12, to allow the body 12 to bepositioned relative to a vertebra, as shown in FIG. 11A, and driven intothe vertebra. While the shape and size of the staple-engaging member 406can vary depending on the shape and size of the staple body 12, in anexemplary embodiment the staple-engaging member includes opposeddeflectable members 408 a, 408 b that are separated by an elongate slot410. The elongate slot 410 extends proximally from the distal-most endof the device 400 to allow the opposed deflectable members 408 a, 408 bto deflect relative to one another. The length of the elongate slot 410can vary depending on the desired flexibility of the deflectablemembers. As is further shown in FIGS. 11B and 11C, the opposeddeflectable members 408 a, 408 b can include a substantially cylindricaldistal portion having a recess 412 formed in a distal surface thereoffor receiving the staple body 12. In the illustrated embodiment, therecess 412 has a substantially rectangular shape for receiving the arms20 a, 20 b formed on the staple body 12, as shown in FIG. 11C.

In use, the staple body 12 can be engaged by the opposed deflectablemembers 408 a, 408 b by placing the deflectable members 408 a, 408 bover the staple body 12, thereby causing the members 408 a, 408 b todeflect around the arms 20 a, 20 b to engage the arms 20 a, 20 b. Thestaple inserter tool 400 can then be manipulated to place the staple 12into a vertebrae. In one embodiment, the handle 404 of the tool 400 canbe impacted to impact the staple body 12 into bone. Alternatively, thefastening element 14 can be used to drive the staple 12 into bone.

Once the staple is implanted in the vertebra, or at least positioned asdesired relative to the vertebra, one or more bone preparation tools canbe inserted through the shaft 402 of the inserter tool 400 to prepare abone hole for receiving the fastening element 14. By way of non-limitingexample, FIG. 12A illustrates an awl 420 inserted through the hollowelongate shaft 402 of the inserter tool 400. The awl 420 is shown inmore detail in FIG. 12B, and as shown it has a generally elongate shaft422 with a proximal handle 424 and a distal bone-penetrating tip 426 forstarting a bone hole. FIG. 12C illustrates the distal end of theinserter tool 400 showing the bone-penetrating tip 426 of the awl 420extending through the central opening in the staple body 12. In use, theawl 420 is inserted through the inserter tool 400 and an impacting forceis applied to the handle 424 to drive the bone-penetrating tip 426 intobone. Consequently, the driving force applied to the awl 420 can be usedto drive the staple body 12 into bone as well.

Once the bone hole is prepared in the vertebra through the staple body12, the staple inserter tool 400 and awl 420 can be removed, leaving thestaple implanted in the vertebrae. A tap 460 can then be used to formthreads within the bone hole, as shown in FIG. 13A, thereby preparingthe bone hole for receiving the fastening element 14. The tap 460, whichis shown in more detail in FIG. 13B, is similar to the awl 420 exceptthat it includes a threaded shaft 462 formed on the distal end thereof.Alternatively, the tap can be inserted through the staple inserter toform threads within the bone hole.

Once the bone hole is prepared using the awl 420, tap 460, and/or anyother tools that may be necessary, the fastening element 14 can beinserted through the staple body 12 and into the bone hole to fixedlysecure the staple body 12 to the vertebra. FIG. 14 illustrates thefastening element 14 about to be inserted into the bone hole using adriver tool 480. This procedure can be repeated to implant additionalspinal anchoring devices one or more adjacent vertebrae. FIG. 15 showstwo spinal anchoring devices 10, 10′ implanted in two vertebrae in apatient's spinal column.

Once a desired number of spinal anchoring devices are implanted, aspinal fixation element, such as tether 50, can be positioned to spanbetween each of the devices. FIG. 16A illustrates tether 50 extendingbetween spinal anchoring devices 10, 10′. A locking assembly can then beapplied to each spinal anchoring device 10, 10′ to lock the tether 50relative thereto. A fastener inserter tool 500 can be used to apply thefastening element, e.g., the washer 16 and locking nut 18, as is alsoshown in FIG. 16A. The exemplary inserter tool 500, which is shown inmore detail in FIGS. 16B and 16C, has a generally elongate shaft 502with a distal end having a substantially cylindrical shape with opposedarms 504 a, 504 b formed thereon. The arms 504 a, 504 b are adapted toreceive and engage the strut 36 of the washer 16, thereby mating thewasher 16, as well as the locking nut 18 which is disposed around thewasher 16, to the inserter tool 500. The inserter tool 500 can then bemanipulated to position the washer 16 and locking nut 18 over the arms20 a, 20 b of the staple body 12.

The fastener inserter tool 500 can also include a wrench 520 that isadapted to be slidably disposed over the fastener inserter tool 500 andthat is adapted to engage and rotate the locking nut 18, as shown inFIGS. 17A and 17B. The wrench 520 is shown in more detail in FIG. 17C,and as shown it has a generally elongate hollow shaft 522 with aproximal handle 524 and a distal socket member 526 formed thereon. Thesocket member 526 includes a socket 528 formed therein and having ashape that corresponds to a shape of the locking nut 18. In an exemplaryembodiment, the socket member 526 includes a hexagonal socket 528 formedtherein for mating with the hexagonal outer surface of the locking nut18. In use, the wrench 520 is inserted over the fastener inserter tool500 until the locking nut 18 is received within the socket 528. Thehandle 524 of the wrench 520 is then rotated to rotate the locking nut18, thereby threading the locking nut 18 onto the staple body 12. As aresult, tether 50 is engaged between the washer 16 and the staple body12 such that it is maintained in a substantially fixed position.Additional locking assemblies can be applied to additional spinalanchoring devices to lock the tether 50 thereto. Tension can be appliedto the tether 50 between each anchoring device prior to or whileapplying the locking assemblies to achieve a desired result. FIG. 18illustrates tether 50 extending between two spinal anchoring devices 10,10′.

While FIG. 18 illustrates a single tether 50 positioned on one side ofthe spine, multiple tethers can be used depending on the deformities tobe corrected. As previously indicated, the tether is preferablypositioned on the concave side of a deformed spinal curve, therebyhalting growth on the convex side of the deformity. Thus, where thespine is curved at multiple locations, multiple tethers can be used. Forexample, three spinal anchoring devices can be placed in the sagittalplane on the concave side of the curve in the spinal column at a firstlevel, and three additional spinal anchoring devices can be placed onthe opposed side of the spinal column at a second level such that thethree additional spinal anchoring devices are placed on the concave sideof a second curvature formed in the spinal column. A tether can thus bepositioned to span between the spinal anchoring devices at the firstlevel, and a second tether can be positioned to span between the spinalanchoring devices at the second level on the opposite side of the spine.Tension can then be applied to each tether and the tethers can be lockedrelative to each spinal anchoring device as previously discussed. Thetension between each vertebra can vary depending on the desiredcorrection, which can be accomplished intraoperatively by tensioning thetethers to achieve the correction immediately, and/or by allowing normalgrowth of the spine to achieve correction by asymmetrically restrictinggrowth using the tether. Once correction has been achieved, the tetherscan optionally be cut to release the tension at one or more levels. Inone embodiment, the tethers can be cut in a minimally invasiveprocedure. Cutting the tethers is particularly advantageous to preventover-correction.

As noted above, the position of each fixation element along thepatient's spinal column will vary depending on the spinal deformitybeing corrected. In other exemplary embodiments, to achieve correctionof a scoliotic deformity in the frontal plane, both tethers can beplaced on the convex side of the curve, with one posterior tether andone anterior tether. The tethers can be mated to the vertebrae byseveral spinal anchoring devices that are implanted adjacent to oneanother within each of several adjacent vertebrae. Tension can then beapplied to both the anterior and posterior tethers by selectivelyfastening the anchoring devices to lock the tethers therein. To correctonly the frontal plane deformity, equal tension is preferably applied toboth tethers, and the degree of tension dictates how much correction isachieved intraoperatively and how much is left to take place duringasymmetric growth restriction.

To achieve correction of a saggittal plane deformity in addition tocorrection of a scoliotic deformity, the anterior and posterior tethersare preferably tensioned differently. To increase lordosis, theposterior tether is tightened more than the anterior tether. To increasekyphosis, the anterior tether a is tightened more than the posteriortether. Similar to correcting the scoliotic deformity, the degree oftension dictates how much correction is achieved intraoperatively andhow much is left to take place during asymmetric growth restriction.

In certain exemplary applications, the implants and instrumentsdescribed herein are designed to be used in a minimally invasivesurgical procedure; thus the dimensions are such that they can beinserted through a portal with an inner diameter of approximately 5 to30 mm, more preferably 15-20 mm. This is particularly important when theimplants are being used to correct a cosmetic deformity, where lengthyincisions would negate the positive cosmetic effect of the correction.

One of ordinary skill in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

1. A spinal anchoring device, comprising: a staple body defining acentral opening formed therethrough and having opposed arms formed on asuperior surface thereof that define a pathway extending across thecentral opening for seating a tether; a fastening element adapted toextend through the central opening formed in the staple body to mate thestaple body to bone, the fastening element having a head extendingbetween opposed arms of the staple and positioned on the superiorsurface of the staple body; and a locking assembly configured to engagethe opposed arms of the staple body such that a tether extending throughthe pathway between the locking assembly and the staple body is engagedby the locking assembly and the staple body.
 2. The spinal anchoringdevice of claim 1, wherein -the central opening of the staple body has asubstantially spherical surface formed therearound for seating acomplementary spherical surface formed on the fastening element.
 3. Thespinal anchoring device of claim 1, wherein the opposed arms extend fromopposed sides of the superior surface, the pathway extending between theopposed arms.
 4. The spinal anchoring device of claim 3, wherein theopposed arms include threads formed thereon for mating withcorresponding threads formed on the locking assembly.
 5. The spinalanchoring device of claim 1, wherein the locking assembly comprises awasher adapted to couple to the staple body such that a tether extendingthrough the pathway is positioned between the washer and the staplebody, and a locking nut adapted to engage the staple body to lock thewasher to the staple body.
 6. The spinal anchoring device of claim 1,wherein the opposed arms on the staple body include threads formedthereon for mating with corresponding threads formed on the locking nut.7. The spinal anchoring device of claim 1, wherein the washer includes astrut extending there across and adapted to be positioned between theopposed arms.
 8. The spinal anchoring device of claim 1, wherein thewasher includes a strut extending there across and adapted to bepositioned between the opposed arms.
 9. The spinal anchoring device ofclaim 8, wherein the head includes a substantially spherical inferiorsurface that is adapted to correspond to a substantially sphericalsurface formed around the central opening of the staple body.
 10. Thespinal anchoring device of claim 1, wherein the head includes a recessformed therein for receiving a tool adapted to drive the bone screw intobone.
 11. The spinal anchoring device of claim 1, further comprising adeformable clip adapted to be disposed around a tether and positionedwithin the pathway such that the locking assembly is adapted to deformthe clip to engage the tether when the locking assembly is mated to thestaple body.
 12. The spinal anchoring device of claim 1, wherein thelocking mechanism includes a washer.
 13. A spinal anchoring device,comprising: a staple having at least one bone-engaging member formed onan inferior surface thereof, and opposed arms extending from a superiorsurface thereof and defining a pathway therebetween for seating atether; a fastening element adapted to mate the staple to bone andhaving a head extending between the opposed arms of the staple andpositioned on the superior surface of the staple; and a locking assemblyconfigured to engage the opposed arms of the staple such that a tetherdisposed in the pathway between the locking assembly and the staple isengaged by the locking assembly and the staple.
 14. The spinal anchoringdevice of claim 13, wherein the locking assembly includes a locking nuthaving threads for mating with corresponding threads formed on theopposed arms of the staple.
 15. The spinal anchoring device of claim 14,wherein the locking assembly further includes a washer adapted to bepositioned between the locking nut and the superior surface of thestaple.
 16. The spinal anchoring device of claim 13, further comprisinga tether-engaging feature formed on at least one of the staple, thefastening element, and the locking assembly.
 17. The spinal anchoringdevice of claim 16, wherein the tether-engaging feature comprises atleast one ridge formed on the locking assembly adapted to engage atether seated in the pathway.
 18. The spinal anchoring device of claim16, wherein the tether-engaging feature comprises a protrusion formed onthe locking assembly such that the protrusion is adapted to alter a pathof a tether seated in the pathway.
 19. The spinal anchoring device ofclaim 13, wherein the locking assembly includes a washer.